Vulcanization system containing a three-component accelerator system

ABSTRACT

Three-component accelerator system for the vulcanization of rubber, one accelerator being 2-(morpholinodithio)-benzothiazole, a second accelerator being a compound such as 2-(morpholinothio)benzothiazole, and a third accelerator being morpholine disulfide.

United States Patent m1 Maxey [451 Uec..3,197

[ VULCANIZATION SYSTEM CONTAINING A THREE-COMPONENT ACCELERATOR SYSTEM [75] Inventor: Frank S. Maxey, Akron, Ohio [73] Assignee: The Goodyear Tire & Rubber Company, Akron, Ohio [22] Filed: Apr. 18, 1972 [21] Appl. No.: 245,263

[52] US. Cl. 260/795 B, 252/182, 260/79.5 C, 260/785, 260/786 [51] Int. Cl. C08c 11/62, C08d 9/00, C08f 27/06 [58] Field of Search 260/795 R, 79.5 B, 785, 260/786, 795, 798, 779; 252/182 [56] References Cited UNITED STATES PATENTS 2,927,099 3/1960 Railsback 260/795 3,557,028 l/l97l Turk 260/5 Primary Examiner-Christ0pher A. Henderson Attorney, Agent, or FirmF. W. Brunner; J. A. Rozmajzl [5 7] ABSTRACT 8 Claims, N0 Drawings VULCANIZATION SYSTEM CONTAINING A THREE-COMPONENT ACCELERATOR SYSTEM N\ R3 This invention relates to an improved accelerator system for the vulcanization of rubber. More particularly 5 are repretemfd below.by sting of Specific radicals it relates to a three component accelerator System any combination of which in structural formula 1 above which provides a vulcanized rubber possessing represents a specific second accelerator. R and R can proved physical properties be the same or different.

Rubber compounders are constantly searching for improved accelerator systems for the sulfur vulcaniza- Where R and R tion of rubber. Such accelerator systems should preferably provide good scorch resistance, reasonable vulca- R R (R -w heter cyclic ring nization rates and adequate physical properties, both g and unaged hydrogen methyl methyl morpholino I methyl ethyl ethyl pyrrolidinyl it is an ob ect of this invention to provide an accelerl5 methoxy isopropyl isopropyl piperidino ator system to be used in the vulcanization of rubber. eihoxy Cyanoethy' cyanoethy' CYClohexumethyleneamin ni r n-butyl n-buiyl 2,6-dimethylmorpholino It is a further ob ect of this invention to provide an acchloro sec.butyl sec.butyl thiomorpholino celerator system which provides, on vulcanization, a g y g y g e gtyllpiperizinyl vulcanizate having improved physical properties. It is eye 0 exy cyco exy i ihhgiggi i g another ob ect of this invention to provide vulcanizable 4-mcthylpiperidino rubber compositions which are capable of being vulcanized to provide improved vulcanizates. Other objects paftlcularly Preferred Second accelfirators are the will become apparent subsequently herein.

The objects of the present invention are accombenlothlallfl dlsqlfide plished by vulcanizing a rubbery composition contain- 2-(morpholmothlo)-benZqth1aZ0-le ing an accelerator system comprising (A) 2- N-(cyclohexyl)-2-ben?othlazoleslulfetlamld8 (morpholinodithio)-benzothiazole, (B) a second accel- N-(t-butyl)-2-benz0th1azolesiilfenamide erator which is a benzothiazole and (C) morpholine di- P Py T Q a 1fid 2-(2,6-d1methylmorpholinothio)-benzothiazole The second accelerator preferably has the following FIN-(methyl)-2-bBn? th1aZ0l@Sulfenamlde structural f l N-(octyl)-2-benzothiazolesulfenamide My 2-(3-methylpiperidinothio)-benzothiazole R N The following compounds illustrate the second accelerator of structural formula I when A is a substituted or C--SA unsubstituted benzothiazole radical.

benzothiazyl disulfide 1 5 (I) 2-(S-chlorobenzothiazolyl) disulfide 2-( 6-nitrobenzothiazolyl) disulfide wherein A is selected from the group consisting of hy- 2-(6 eth9XYbenZth'aZ1Yl) dlsulfide drogen 40 When A is hydrogen the second accelerator of struc- V V tural formula I can be a compound such as Z-mercap- R tobenzothiazole.

R2 3 R2 when A'iS g A N\ S0 and -N\ R2 R3 s R3 u C N/ R1 i R wherein R and R are selected from the group consistillustrative compounds are as f ll w g of hy rogen, ni chloro, alkyl radicals having 2-benz0thiazyl N,N-dimethylthiocarbamoyl sulfide from 1 to 4 Carbon atoms and radicals having 2-benzothiazyl N,N-diethylthiocarbamoyl sulfide f 1 t0 4 Carbon atoms and Whefeln and are 2-benzothiazyl N,N-diisopropylthiocarbamoyl sulfide selected from the group consisting of alkyl radicals having from 1 to 6 carbon atoms, cycloalkyl radicals havwell known in the art and can be prepared by we" mg from 5 to carbon atoms aralkyl radicals having known processes such as that described in U.S. Pat. No. from 7 to 13 carbon atoms and aryl radicals having 2 837 519 from 6 to 12 Carbon atoms and R2 and R3 can be 9 q The second accelerators are well known in the art through a member selected from the group consisting and can be prepared by well known processes such as of and cns.mute.with the those described in us. Pat. Nos, 1,631,871; 2,024,575; tached nitrogen group of heterocyclic radical. Where The 2-(morpholinodithio)-benzothiazole (MDB) is 2,045,888; 2,l9l,656 and 2,615,893. A 4,4'-Dithiomorpholine is also well known and can be prepared, for example, according to the process def" scribed in U.S. Pat. NO. 2,343,524.

1 The accelerator system of the present invention is R used in vulcanizable rubber compositions, corn 7 pounded and uncompounded, along with 0.00 to 3.25 R can also be hydrogen. parts by weight of free sulfur based on 100 parts by Specific examples of the derivative of the second acweight of uncompounded rubber. The MDB must comcelerator conforming to above recited structural forprise 20 to percent (preferably 30 to 60 percent) of mula I when A is the total three-component accelerator combination.

1 3 The second accelerator comprises to 60 percent (preferably to percent) of the combination. The morpholine disulfide also comprises 10 to percent (preferably 20 to 40 percent) of the combination.

The accelerator level varies from 0.50 to 5.50 parts by weight per 100 parts by weight of uncompounded rubber. Improvements in physical properties are obtained at low sulfur levels and in sulfurless systems, i.e.,

from 0.00 to and including 1.25 parts of free sulfur based on 100 parts by weight of uncompounded rub ber. Improvements are also obtained when a high sulfur level (above 1.25 parts and up to 3.25 parts of free sulfur) is used. The present invention, however, is generally most beneficial at low sulfur levels, such as 0.10 to 1.25 parts.

The sum of the three-component accelerator system and the sulfur ranges from 2.25 to 5.50 parts by weight per 100 parts by weight of rubber.

The accelerator can be compounded into the rubber by any conventional method, such as by addition to the rubber on a mill or a Banbury when the rubber is a solid. The rubbers can contain any conventional compounding ingredients such as carbon black, zinc oxide and even other accelerators to the extent that the accelerators do not interfere substantially with the im-' provement offered by the accelerator system of the present invention.

The rubber vulcanizates prepared using this accelerator system can be used in any of their normal applications, such as in pneumatic vehicle tires and industrial products.

Some of the following examples are intended to illustrate but not to limit the practice of the preSF L .inven:

Formulations Ingredients A B C Natural 100.0 SBR 1500 100.0

; 67/33 butadiene-l.3/

acrylonitrile 100.0

. zinc oxide 5.0 3.0 5.0 stearic acid 1.0 2.0 1.0 amine antioxidant 1.0 1.0 1.0 HAF black 40.0 40.0 40.0 petroleum softener 3.0 dibutyl phthalate 5.0 processing oil 5.0

Formulation A was used in preparing Examples 1 to 7. Formulation B was used in preparing Examples 8 to 14. Examples 6, 7, and 14 illustrate the practice of the present invention. It is understood in each of the fol- ,lowing examples that in addition to the sulfur and accelerator amounts indicated, the rubbers also contained the ingredients indicated in the non-productive formulations recited earlier herein.

Examples 1 to 7 (High Sulfur Natural Rubber) Sulfur 2.75 2.75 2.75 2.75 2.75 2.75 2.75 MDB(1) 0.60 0.30 0.30 0.20 MBTS(2) 0.70 0.20 MOR(3) 0.60 0.30 0.15 DTDM(4) g 0.60 0.15 0.20 OCT(5) v 20 28 20 40 23 22 26 Scorch(6) 30 30 30 30+ 30+ 30+ 30+ T(7) 290 256 275 254 297 307 298 15(7) 600 660 600 580 620 600 590 300M(8) 99 103 103 102 Shore A(8) 60 58 61 58 61 60 61 Tear(9) 106 86 99 63 95 106 110 Aged(10) E 250 210 260 210 290 320 310 Aged Shore A 60 56 58 63 63 61 62 Flex(11) Orig. 183 153 148 166 171 190 188 Aged 133 120 123 100 146' GF( 12) Orig. 17.0 20.0 16.8 28.3 19.1 18.8 16.3

Aged 21.8 23.2 21.9 33.4 21.1 21.4 18.4 Rebound (1) 2-( morpholinodithio)-henzothiazole (Z) benzothiazyl disulfide (3) 2-(mnrpholinothio1-henzothiazo1e (4) 4.4'-dithiomorpho1ine (5) Optimum cure time (OCT) was determined using the Monsanto Rhcometer, 100 CPM 3" are, 143C.

(6) Mooney Search at 120C..A5.

(7) TIE is a measure of the tensile strength and elongation (Kg/cm and "k (t1) 300M is a measurement of the stress at 300% elongation. Shore A is a measure of the hardness as measured by the Shore A durnmeter. (9) Crescent tear test (Die C).

( l0) Aged TIE is tensile and elongation properties measured after the samples had been aged in a hot air oven for 70 hours at 100C.

(11) Flex test is the Goodyear 66'] Flex test. Original tests were run at 25C. while aged refers to the flex test results run after the samples had been aged in a hot air oven for 22 haunt at 100C.

(12) Goodrich FlexometenATPC.)

The results in Examples 1 to 7 indicate that systems of the present invention (Examples 6 and 7) were superior to any of their individual components alone. Note particularly the tear, aged T/E and flex.

Example 14 illustrates the superiority of the system of the present invention. Note particularly the Aged T/E, Aged Flex and Rebound, but most particularly note the Compression Set.

Examples 8 to 14 (Low Sulfur-8BR) Sulfur 0.3 0.3 0.3 0.3 0.3 0.3 0.3 MDB 3.0 1.5 1.5 1.0 MOR 3.0 1.5 1.5 1.0 DTDM 3.0 1.5 1.5 10 OCT 33 43 50 33 24 3O 25 Search 30+ 30+ 30+ 30+ 30 26 238 189 224 248 230 210 254 E 530 700 650 560 560 670 570 300M 98 49 58 105 90 68 98 Shore A 62 60 58 61 60 60 64 Tear 39 44 42 42 41 41 44 Aged T 188 193 210 219 210 200 232 E 420 620 570 490 480 480 510 Aged 300M 112 63 101 119 120 119 147 Shore A 66 63 57 66 60 64 66 Flex Orig. 240 240+ 240 240+ 240+ 240+ 240+ Aged 34 218 227 210 188 138 217 GF Orig. 34.2 77 46.5 34.2 38.6 60.1 28.3 Aged 32.4 67 33.2 31.6 36.2 40.1 27.2 Rebound 25C. 62 58 58 63 60 60 66 100C. 74 58 64 72 72 73 77 Set (13) 60 43 48 20.7

( 13) Percent recovery after being compressed to 25 percent of its original height and held for 22 hours at 100C Examples 15 to 121 (SBR-No Sulfur) Sull'ur 0.0 0.0 0.0 0.0 MOR 1.5 TMTD( 14) 3.0 MDB 1.5 2.5 1.5 DTDM 3.0 1.0 2.5 MBTS 3.1) 1.0 OCT 40 48 44 30 Scorch 30 30+ 30+ 30 T 163 236 242 232 E 310 550 560 520 300M 157 98 101 98 Shore A 63 65 61 Tear 24 39 46 40 Aged T 145 200 222 216 E 210 350 520 470 Aged 300M 162 120 122 Shore A 69 67 63 62 Flex I Orig. 28 240+ 240+ 240 Aged 14 109 240 158 (SF Orig. 28.7 28.8 31.6 28.4 Aged 22.9 24.8 30.4 27.0 Rebound 25C. 64 62 64 100C. 77 81 77 Set 37 51 52 37 (14) leirumcthylrhiuram disullidc ponents alone possessed superior Compression Set and Goodrich Flexometer characteristics.

Again using formulation A but in a sulfurless system 25/15/10 and 1.0/1.5/2.5 MD'B/MOR/DTDM systems were compared with a 3.0/3.5 MOR/DTDM system. Aged T/E. Flex, Goodrich Flexometer and Compression Set characteristics for the three-component systems were superior.

Using formulation 13 and 1.70 parts of sulfur a 0.33/0.33/0.34 MDB/MOR/DTDM system possessed better aged T/E and aged Flex than any of its components alone or 0.5/0.5 MDlB/MOR or 0.5/0.5 MDB/DTDM systems.

Using formulation C and 1.75 parts of sulfur a O.27/0.27/0.27 MDB/MOR/DTD'M system possessed superior aged T/E, Compression Set and aged Flex when compared with each of its individual components alone or 0.40/0.4O MDB/MOR or 0.40/O.4O MDB/DTDM systems.

Using formulation C and a 0.30 part sulfur level a 1.0/1.0/1.0 MDB/MOR/DTDM system provided superior Compression Set and Flex both aged and unaged when compared with each of its individual components alone or a 1.5/1.5 MDB/MOR or 1.5/1.5 MDB/DTDM system.

Using formulation C and no sulfur 1.25/l.00/1.25 and l.50/1.50/1.50 MDB/MOR/DTDM systems possessed aged T/E and Compression Set superior to a 2.5/1.5 MDB/DTDM system.

Overall, all of the three-component systems tested have what could be considered an overall superior combination of physical properties. Although sometimes inferior in some properties, the vulcanizates prepared using the three-component system were always superior to any system with which it was concerned in at least one of the following properties: aged T/E, Flex (original or aged), Compression Set or Goodrich Flexometer.

The aforementioned properties are quite important in various applications. Compression Set is important with regard to seals and gaskets. Flex is important in belt and tire applications. Aged T/E is important with regard to tires and high temperature belts and hose. Goodrich Flex properties would be considered where a polymer was to be used in a motor mount.

The other accelerator compounds described earlier herein could have been substituted for their counterparts in the preceding working examples to produce vulcanizates with a superior combination of physical properties.

Likewise, various other polymers could have been substituted for those used in the preceding working examples, such as cis-1,4 polyisoprene, cis-l,4 polybutadiene or ethylene/propylene/ 1,4-hexadiene polymers. Naturally, as the rubber is changed or a different loading is used, standard changes in the compounding recipe would be made to obtain optimum results.

The sulfur vulcanizable rubbers that will benefit from this invention include natural rubber and synthetic rubbers and mixtures thereof. Synthetic rubbers that can be improved by the practice of the present invention include all diene rubbers including the following elas'tomers, either alone or in blends, cis-l,4, polyisoprene, polybutadiene, including cis-l,4 polybutadiene, rubbery copolymers of 1,3-dienes such as 1,3-butadiene,

isoprene or 2,3-dimethyl-1,3-butadiene with other monomers, for example, styrene, acrylonitrile and methyl methacrylate. Ethylene propylene terpolymers (EPDM), i.e., with a non-conjugated diene, for example, terpolymers of ethylene propylene and dicyclopentadiene or 1,4-hexadiene or ethylidene norbornene can also benefit from the present invention. For maximum benefit, the EPDM polymer should be classified as fast curing or ultra fast curing. In fact, for best results any polymer used should vulcanize readily. Chlorinated polymers which possess unsaturation such as polychloroprene will show improved vulcanizate properties when used in the practice of the present invention as will polyalkcnamers such as polyoctenamer prepared by a ring opening process involving cyclooctene. Although it is generally preferred that the mole percent unsaturation of the polymer be at least 1.0 percent to 2.0 percent and higher, the source of the double bond must be considered. For example, EPDM polymers prepared using ethylidene norbornene as the termonomer vulcanize more readily than an EPDM polymer prepared using dicyclopentadiene as the termonomer.

While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in this art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.

What is claimed is: g y

l. A sulfur vulcanizable rubber containing 0.00 to 3.25 parts by weight of free sulfur per 100 parts by weight of rubber and 0.5 to 5.50 parts by weight per 100 parts by weight of rubber, of an accelerator system comprising A. Z-(morpholinodithio)-benzothiazole. B. at least one benzothiazole accelerator having the following structural formula wherein R and R are selected from the group consisting of hydrogen, nitro, chloro, alkyl radicals having from 1 to 4 carbon atoms and alkoxy radicals having from l to'4 carbon atoms and wherein R is selected from the group consisting of alkyl radicals having from 1 to 6 carbon atoms, cycloalkyl radicals having from 5 to 12 carbon atoms, aralkyl radicals having from 7 to 13 carbon atoms and aryl radicals having from 6 to 12 carbon atoms, wherein R is selected from hydrogen and the radicals for R and R and R can be joined through a member selected from the group consisting of CH O- and S- to constitute with the attached nitrogen group a heterocyclic radical and C. 4,4-dithiomorpholine wherein the weight ratio of A/B/C is 20 to /10 to 60/10 to 60 based on parts by weight of A, B and C, and wherein the total weight of sulfur plus accelerator system is from 2.25 to 5.50 parts by weight per 100 parts by weight of rubber.

2. A sulfur vulcanizable rubber containing 0.00 to 3.25 parts by weight of free sulfur per 100 parts by weight of rubber and 0.5 to 5.50 parts by weight per 100 parts by weight of rubber, of an accelerator system comprising A. 2-(morpholinodithio)-benzothiazole,

B. at least one benzothiazole accelerator selected from the group consisting of 2-(morp'holinothio)-benzothiazole,

N-(cyclohexyl)-2-benzothiazolesulfenamide,

N-( t-butyl )-2-benzothiazolesulfenamide,

N,N-(diisopropyl)-2-benzothiazolesulfenamide,

2-(3,-dimethylmorpholinothio)-benzothiazole,

N,N-( diethyl )-2-benzothiazolesulfenamide,

N-(octyl)-2-benzothiazolesulfenamide, and

2-(3-methylpiperidinothio )-benzothiazole, and

C. 4,4'-dithiomorpholine wherein the weight ratio A/B/C is 20 to 70/10 to 60/10 to 60 based on 100 parts by weight of A, B and C, and wherein the total weight of sulfur plus accelerator system is from 2.25 to 5.50 parts by weight per 100 parts by weight of rubber.

3. The sulfur vulcanizable rubber according to claim 1 wherein R is hydrogen.

4. The sulfur vulcanizable rubber according to claim 1 wherein the sulfur level is from 0.10 to 1.25 parts.

5. The sulfur vulcanizable rubber according to claim 1 wherein the sulfur level is from 1.25 to 3.25 parts.

6. The sulfur vulcanizable rubber according to claim 1 containing as an accelerator a compound selected from the group consisting of N-(cyclohexyl)-2-benzothiazylsulfenamide and 2-(morpholinothio)- benzothiazole.

7. The sulfur vulcanizable rubber according to claim 1 wherein A comprises 30 to 60 percent, B comprises 20 to 40 percent and C comprises 20 to 40 percent by weight of the three-component accelerator system.

8. A process of preparing a rubbery vulcanizate comprising heating the sulfur vulcanizable rubber of claim 1 at a vulcanizing temperature.

mas?" v 'A w STATES PA'IENT OFFICE T CA E OF 'CORREC'NON hcenc no. 3, 5 ,25 mud December 3, 197

In nt Frank Maxey It in certified that error appears in the above-identified patent and that aid Letter: Patent are hereby corrected as shown kelw;

Column 5, in-the table entitled, "Examples 8 to lPl-(Low v Sulfur-8BR)" Example 11, last figure reads +3" and ,should read +O Examfile 12,, last figure reads l-8" and should read 3 j-*Ex ample l3, last figure reads "2097" and should r- 'e ad 8 Example 1%, last figure was omitted but "should read"-'---207 Signed and sealed thiiw-llthday of March 1975.

(SEAL) Attest:

c. MARSHALL DANN RUTH C. MASON Commissioner of Patents' Attesting Officer and Trademarks Po-wso Patent No. 3

UNITED STATES PATENT o FIcE mud December 3, 197

Invcntoflfl Frank 'S Maxey It in certified that error appears in the above-identified patent and that aid Letter. Patent an hereby corrected as si aown below;

Column 5,

(SEAL) Attest:

RUTH c. MASON, Attesting Officer in the table entitled, "Examples 8 to l KLow Sulfur-8BR)" Example 11, last figure reads +3" and should read +0 Examfile 12,, last figure reads +8" and should read 3 --v; f--Ex ample 13, last. figure reads "20?" and should read 8 Example 1 last figure was omitted but "should read"-'- 2007 Signed and sealed thifir-llth day of March 1975.

c. MARSHALL DANN Commissioner of Patents and Trademarks 

1. A SULFUR VULCANIZABLE RUBBER CONTAINING 0.00 TO 3.25 PARTS BY WEIGHT OF FREE SULFUR PER 100 PARTS BY WEIGHT OF RUBBER AND 0.5 TO 5.50 PARTS BY WEIGHT PER WEIGHT OF RUBBER, OF AN ACCELERATOR SYSTEM COMPRISING A. 2-(MORPHOLINODITHIO)-BENZOTHIAZOLE, B. AT LEAST ONE BENZOTHIAZOLE ACCELERATOR HAVING THE FOLLOWING STRUCTUAL FORMULA
 2. A sulfur vulcanizable rubber containing 0.00 to 3.25 parts by weight of free sulfur per 100 parts by weight of rubber and 0.5 to 5.50 parts by weight per 100 parts by weight of rubber, of an accelerator system comprising A. 2-(morpholinodithio)-benzothiazole, B. at least one benzothiazole accelerator selected from the group consisting of 2-(morpholinothio)-benzothiazole, N-(cyclohexyl)-2-benzothiazolesulfenamide, N-(t-butyl)-2-benzothiazolesulfenamide, N,N-(diisopropyl)-2-benzothiazolesulfenamide, 2-(3,6-dimethylmorpholinothio)-benzothiazole, N,N-(diethyl)-2-benzothiazolesulfenamide, N-(octyl)-2-benzothiazolesulfenamide, and 2-(3-methylpiperidinothio)-benzothiazole, and C. 4,4''-dithiomorpholine wherein the weight ratio A/B/C is 20 to 70/10 to 60/10 to 60 based on 100 parts by weight of A, B and C, and wherein the total weight of sulfur plus accelerator system is from 2.25 to 5.50 parts by weight per 100 parts by weight of rubber.
 3. The sulfur vulcanizable rubber according to claim 1 wherein R3 is hydrogen.
 4. The sulfur vulcanizable rubber according to claim 1 wherein the sulfur level is from 0.10 to 1.25 parts.
 5. The sulfur vulcanizable rubber according to claim 1 wherein the sulfur level is from 1.25 to 3.25 parts.
 6. The sulfur vulcanizable rubber according to claim 1 containing as an accelerator a compound selected from the group consisting of N-(cyclohexyl)-2-benzothiazylsulfenamide and 2-(morpholinothio)-benzothiazole.
 7. The sulfur vulcanizable rubber according to claim 1 wherein A comprises 30 to 60 percent, B comprises 20 to 40 percent and C comprises 20 to 40 percent by weight of the three-component accelerator system.
 8. A process of preparing a rubbery vulcanizate comprising heating the sulfur vulcanizable rubber of claim 1 at a vulcanizing temperature. 